MythBusters Interview: Adam and Jamie Build a Duct Tape Bridge

In last season's duct tape special, MythBusters Jamie Hyneman and Adam Savage constructed a boat out of duct tape—and it didn't sink. In tonight's episode, airing at 9 pm on the Discovery Channel, the two build a 108-foot-long bridge out of the versatile material and suspend it across a 50-foot-deep empty pool. But will they be able to cross it? Hyneman and Savage take PM behind the scenes of the episode; check back tomorrow to hear more about what the guys learned from their experiment.

Where did you get the idea to build a duct tape bridge?

ADAM SAVAGE: The idea for the duct tape bridge came almost immediately after we were finished sailing the boat around the bay [last season]. We were thinking, what's next, what else could we do? And we had two or three ideas; the bridge was the one we chose for the next bust. We even have a better idea for the next duct tape special.

JAMIE HYNEMAN: We could just keep going on the duct tape thing. It'll never run out.

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So is the stuff you used just a regular, standard-issue duct tape?

ADAM SAVAGE: It is. Nashua makes about ten different kinds and it's a middle grade that we keep on settling on as our favorite.

JAMIE HYNEMAN: And there is heavier stuff. I think probably in any of the experiments that we've done, we could've put heavier stuff to use to our benefit, but we're trying to show something that's not unusual. It's a standard heavy-duty duct tape.

How much of what you learned about duct tape strength and capabilities for building the boat were you able to use again for the bridge?

JAMIE HYNEMAN: I think we've learned a lot about how to handle it. The trick with that boat was putting the first layer with the adhesive side out and then the second layer with the adhesive layer in and precisely lining it up. With the bridge it was similar. We knew that over that length duct tape is kinda hard to control so we didn't even try. Adam built this rig to pull out ten strands at a time and we didn't make em really messy but we did sort of let them go where they were gonna go and kind of bundled them up because the strength in this case was about the same.

Interesting. I was going to ask about thatbecause when you guys were building the boat, there was a definite order to the way you laid out the tape. And in this case you just sort of clumped it together.

JAMIE HYNEMAN: Yeah, this was all about tensile strength. And so given the amount of tape that we had to usewhat was it?

ADAM SAVAGE: Two hundred rolls of duct tape.

JAMIE HYNEMAN: Yeah, 200 rolls of duct tape over 108 feet. Why fight it, you know? Let it do what it wants to do.

ADAM SAVAGE: It's indicative of how we work with a lot of the materials we end up working with on the show is that you can either go pretty or you can go crunchy. Both have their utilities and both have their advantages and disadvantages. And for the bridge, going crunchy and turning this stuff into basically glorified rope and stringing it together turned out to be really quite effective.

How long is a single roll of duct tape?

ADAM SAVAGE: About 60 yards, 180 feet.

I was going to ask if you guys were worried at all about the structural weaknesses of attaching one roll to another, but I guess you didn't really have to think about that if the distance you had to span was 108 feet.

ADAM SAVAGE: Actually, one of the plans that I wanted to try and do was to find a span that was like 190 feet long so it would be clear we couldn't use a single piece of duct tape for the span of the bridge. But we ran into location limitations there and realized the difference was one that was more interesting to us intellectually than necessary for the narrative of the show.

When you finally figured out that you were going to do a bridge, how did you come up with a plan of attack in terms of what design to go with?

ADAM SAVAGE: We actually had two totally different viewpoints about how it would go. In the beginning, Jamie and I often talk in the abstract, arguing back and forth for different approaches. Often we don't conclude something out of those conversations but we conclude a method of proceeding. So we bandied back and forth for about a day and then we just went down to the shop and started mucking around with duct tape until something became clear.

JAMIE HYNEMAN: I recall specifically going through the exercise of thinking that what duct tape has is tensile strength and it doesn't have any compressive strength or anylike if you were doing a keystone kind of a structure, for example, it wouldn't work. It's all effectively just rope. Going on that premise leaves you with a suspension bridge. There's not a whole lot of other choices involved. So that was the direction that we went.

Why did you opt to not do the weaving thing? You did that a little bit when you were first testing.

ADAM SAVAGE: It didn't seem necessary for the overall construction of the bridge. Again, it's balancing all the elements of time and effectiveness. And while it worked somewhat well in the shop's limited space, I don't think it would have added any necessary structure to the bridge.

JAMIE HYNEMAN: Yeah. It was all about that simple thing again, the tensile strength of it.

ADAM SAVAGE: It was an attempt to add some compressive strength to the floor we were going to walk on, you know?

JAMIE HYNEMAN: What we did, as you can see in the design, is went with a walkway that was only as wide as it had to be to accommodate our feet. You know, like even barely wide enough to even put our feet sideways on it. So it was kind of like a flat rope. And with it done that way, we didn't really have to worry about whether it drooped or became like a bag as we walked across it.

Was there any behind-the-scenes deliberation that viewers didn't get to see?

JAMIE HYNEMAN: We did tests that showed that just three strips of tape were capable of supporting one of us. We used 200 rolls, and most of those rolls were in the walkway. We could've done it with much less. The tighter that you pull a bridge like that, the straighter the line would be that's going across the chasm and it becomes a significantly larger load on the tape the more that you pull on it. You know, like the tauter it is. It's a question of leverage on the middle of the bridge.

And so while we did our experiment here across 30 feet with three strips of tape and that was sufficient, expecting three strips of tape to hold us going across a bridge that's 100 feet would be unrealistic because the leverage is so much greater on it. But dialing in on exactly how much it would hold as a part of that was hard for us. We have a couple of engineers here on staff, and it's a more complex thing than it might seem to be able to estimate exactly how many strips of tape would be required to support a person across that span.

It changes as you put load on it, the leverage. It's not a static thing. The less straight the thing becomes, the more the tensile strength changes. So it was sort of a dynamic thing that we didn'tfrankly, in our sort of seat-of-the-pants engineering approach, we couldn't find a straightforward way of really dialing in on that so we just overdid it a bit. Since we had all these cases of tape, we figured, why not?

How long do you think it would've taken you to build it by hand? Obviously that rig helped speed up the process a lot.

ADAM SAVAGE: I'd say that probably saved us a couple of days in the overall build, maybe a day.

JAMIE HYNEMAN: Yeah, at least a day. I don't think the thought actually ever crossed our minds that we would do it any other way. We might have strung them out by putting them all on a single axle instead of having the ten axles suspended above each other, which was Adam's idea ... and it turned out to be quite effective. I had my hesitations about it because all those little rollers and everything are a little difficult to set up, but Adam cranked through it and it was clearly the best way to do it.

You had to make some last-minute modifications to the bridge too, once you got it on-site.

ADAM SAVAGE: You know, in all of this there's a lot of moving parts. There's the span itself, but then what order do you make the span in and attach it to where it's going to go? The normal way you might make a rope bridge is to just start stringing rope across the span and then bind it together. We didn't have that luxury, we wanted to build the thing in its entirety. And this is kind of another indicative way that we solve problems. Knowing that this was a tricky thing, we went out on-site, we took careful pictures and measurements of the stuff we were going to mount it to on-site and then the whole time we were working on the bridge and doing ideation on it, we were talking about ways of attaching. And we went through probably about a dozen different ideas before coming across what was really the simplest possible way to do it. The ideas were more like different orders of doing things. A lot of times the order that you do things in is absolutely critical.

JAMIE HYNEMAN: We could've built the thing entirely out on-site but it would have been much slower because having to suspend ourselves with some other kind of means while we're constructing it would've been very tedious, it would have taken many times longer, in fact. And so we opted to do it on the ground and then pull it into place.

Will Jamie and Adam make it across their duct tape bridge? Watch the episode tonight to find out, and check PopularMechanics.com tomorrow morning to hear what the guys learned from their experimentand what's the most terrifying thing they've done on MythBusters so far.